Suko Paste hose pipe extruder extrusion machine for the production of ho...

Suko ptfe plastics Paste hose pipe extruder machine. Mainly used for the production of hoses, pipes, medical piping catheter tubing. WhatsApp/ phone: +8619975113419 mail: info@ptfe-machinery.com https://ptfe-machinery.com/project/polymer-plastic-ptfe-paste-hose-extruder-machine/ https://www.sukopolymer.com/ptfe-plastic-paste-extruder-machine/

Extrusion process of PTFE insulated wire

Ptfe is one of the types of fluorine plastic, used for processing and insulation layer, as a result of ptfe in melting point 327 ℃, and higher than the melting point 360 ℃ using disposable push extrusion sintering molding methods, process is more complex, process quality control involves many factors, once the control is not good, can make the extrusion process to or appear all sorts of quality problem; Once the extrusion and sintering are not successful, it will cause the material part or all scrap, ptfe price is expensive, so it has caused a big waste. Therefore, it is necessary to control the extrusion process of ptfe reasonably, comprehensively and effectively, which is a necessary condition to ensure product quality and reduce waste.

Based on the application and processing practice of ptfe material in electric wires and cables and the practical experience, the paper gives a brief overview of ptfe insulation extrusion process, hoping to help production technicians to make correct selection and control in ptfe extrusion process.

Technological process：                                                                                   

1. Sieve F4 powder    

                                                         

Ptfe powder is the powder particles after polymerization, soft, strength is very small, when in packaging container stored easily by weight or turbulence vibration in transit in the cluster, blending uneven phenomenon, so before mixing must adopt certain specifications of the mesh screen to sieve of ptfe powder, filter out larger knot cooking starch material, the specifications of the mesh screen in 8 and 12 mesh is advisable. If the agglomeration is serious, the powder should be placed in a lower temperature, after a period of time, if the agglomeration shows signs of loosening, then screening. The powder should be stored in a low temperature environment, and should be handled gently in the process of handling, so as to avoid severe agglomeration of ptfe powder and it cannot be used. In addition, environmental hygiene should be ensured and impurities or dust should not be mixed into ptfe powder. Due to the strong electrostatic adsorption of ptfe powder, it is easy to adsorb air or small impurities and dust around, so to keep the environment clean without dust, the packaging container surface should be clean before opening the cover

2. Toner or pulp treatment

When insulation needs coloring for identification, a certain proportion of toner or slurry should be added to ptfe powder. Toner is after fine grinding of high temperature resistant organic or inorganic pigment powder, easy to absorb moisture, agglomeration, so in advance should be heated treatment, remove moisture, and screen, filter out the larger particles. Generally, 180 and 200 mesh screen specifications are appropriate. If the screen screen is smaller than 180 mesh, then the pigment particles after filtering are larger, which is not conducive to the insulation performance of the insulation layer. The screen mesh is more than 200 mesh. Although the insulation performance of insulation layer is guaranteed, it is difficult to filter. Color paste is a mixture of toner and oily liquid, toner in oily liquid suspension state, but stationary for a period of time will precipitate, so before use should be shaken and mixed, so that the precipitate toner particles evenly suspended in oily liquid for use.

3. The ingredients

Batching is an important preparation before mixing, according to the ratio of polytetrafluoroethylene powder and extrusion aid, or color powder or color paste ready, after the mixture.

There are more kinds of extruder, such as yan 20 aviation gasoline, toluene, petroleum ether, or other volatile solvent oil, organic solvent, etc., different extruder volatilization speed is different, according to the actual situation of the equipment, extrusion speed to choose the appropriate extruder. The extrusion assistant volatilizes too fast, although it can shorten the drying time and improve the extrusion speed, it requires strict operation time for the preparation before extrusion, and the preparation operation time should not be too long, otherwise the extrusion assistant of the blank will be ineffective due to excessive volatilization .Extruder is too slow to evaporate, and although there may be sufficient preparation time, the drying time must be extended or higher requirements for the equipment capacity are required. The proportion of extruder should be 18% and 23%, and should be adjusted according to the specifications of the conductor, insulation layer thickness, extrusion speed and extrusion pressure. Generally, the wire specification is larger, the insulation thickness is thicker, the extrusion speed is faster, the compression is smaller, the proportion of the extruder can be appropriately small; On the contrary, the wire specification is smaller, insulation thickness is thinner, extrusion speed is slower, compression is larger, the proportion of the extruder can be appropriately larger.

Toners cost less and are still commonly used today. Using pigments to dye, teflon insulation dispersion in toner as paste, toner and ptfe powder is dry mixing, and toner additives and relatively little, easy to cause mixing cluster, dispersion is poor, is not easy to mix, will lead to serious existence chromatism different part of insulation, so its size as small as possible when choosing toner requirements, general imported toner quality is better. In the toner mixing, should choose the pigment powder temperature tolerance above 400 ℃, otherwise after high temperature sintering (sintering temperature generally basic in 350, 400 ℃) may appear the product fading phenomenon. Generally, inorganic pigments have good high-temperature resistance, while organic pigments have poor high-temperature resistance. Therefore, the use of inorganic pigments as toner is more reliable, but its environmental protection is poor. The matching ratio of toner is generally not more than] %, in the actual production can be according to the type of toner, toner quality, color requirements, insulation layer thickness, etc.

Although the cost of color paste is high, it is conducive to the uniformity of the mixture and is an ideal choice, which can effectively ensure product quality, simple operation, high efficiency and less waste. When mixing the color paste, the color paste can be added to the extrusion aid and premixed evenly. Due to the relatively large amount of extruder, it is wet mixed with ptfe powder, so there is no problem of toner agglomeration, and the dispersion is very good, it is easy to mix evenly. The proportion of color paste is generally between 0.3% and 0.5 ‰, with 3 ‰ being the majority. Only a few special cases require the proportion of 0.5 ‰.When the insulation layer edge layer thickness is relatively thin, the proportion of color paste should be appropriately increased by 0.1%, 0.2.

4. The mixture

Mixing is to mix polytetrafluoroethylene powder with extrusion aid, or color powder or color paste evenly, to ensure that the extrusion insulation lubrication and color uniformity. In order to facilitate uniform mixing, the volume of general mixing bottle (wide mouth bottle) is appropriate to 4, 5 liters, the loading quality is about 800, 1 000 g, the loading volume accounts for about 2/3 of the mixing bottle volume is good, so there is enough space for mixing.

The natural color mixture (mainly used to extrude the insulation of radio frequency cable) does not need to add toner. When mixing, put ptfe powder into mixing bottle first. Used in to make people try not to contact with mixing bottle of bottle wall, in person to squeeze aid available clean sheet tool will gently mixing in a bottle the center of the surface of ptfe powder to bottle wall, make its surface center to form a depth of about 2, 3 c of conical hole, then people directly used in a certain proportion in the taper hole; After that, the mixing bottle shall be capped and strictly sealed to prevent the extruder from volatilizing. Firstly, the mixing bottle shall be shaken and mixed manually for no less than 5 minutes, and then the mixing bottle shall be placed on the mixing machine to swing and roll for more than 30 minutes until the mixing is even.

5. Compact

The effect of pressing (material) billet is to press loose porous polytetrafluoroethylene powder into a relatively compact material billet, eliminating the pores and air contained in it for extruding use. Generally should be in the environment of 20 ℃ above the blank pressing, will be homogenized powder slowly pour into the pressure cylinder cylinder, at the same time should ensure that the heart rod and pressure cylinder cylinder concentric, and gently shake the pressure cylinder in the material surface, and then add pressure cover on it. The pressure should be appropriate, too much or too little will affect the extrusion quality. If the pressure of the blank is too large, the extruder is easy to be overpressed, and the lubrication performance during extrusion is reduced, the extrusion pressure is increased, and the shear stress of the material is larger, leading to excessive fibrosis, which is not conducive to the stability of the outside diameter of the extrusion insulation, and the shrinkage rate of insulation sintering is larger, which is also easy to cause insulation cracking.

6. Squeeze out

The preparation work for ptfe insulation extrusion mainly includes selection of compression ratio, preheating and heating of extrusion cylinder and die, adjustment of needle gap between die sleeve and die core, charging blank, conductor inspection, conductor piercing, adjustment of thread tension, combination sealing of machine head and extrusion cylinder, etc., which will be introduced in the following.

The compression ratio of different brands of ptfe powder during extrusion is also different. the proper compression ratio should be determined according to the properties of ptfe powder to ensure the process performance and quality during extrusion. Extrusion compression ratio refers to the ratio between the annular area of the extrusion die and the annular area of the blank. Generally, extruder cylinders are divided into three sizes: small, medium and large. The diameter of small cylinder is about 38 mm, medium cylinder is about 50 mm, and large cylinder is about 65 mm.In the actual production, the specifications of the extruder cylinder should be selected according to the sectional area of the extruder insulation layer.

In order to maintain a stable temperature of the blank and facilitate the volatilization of the extruder after extrusion, the extrusion cylinder and mold should be preheated properly. The preheating temperature of the extrusion cylinder should be 30 or 40 ℃, and the preheating temperature of the mold should be 50 or 60 ℃.

The extrusion should be according to the specifications of the corresponding matching mold and according to the location of the assembly, and the mold sleeve bearing line neck population and needle tube between the distance (gap) to the appropriate position. Too large or too small clearance will affect the quality of the extruded insulation layer. If the gap is too small, the velocity of extrusion of ptfe material to the outside of the mold will be accelerated, and the material will be excessively cut, leading to excessive fibrosis, resulting in the decrease of the transverse strength of insulation layer, the product is prone to longitudinal cracking or internal cracks of insulation, and the insulation and conductor coating is not tight (there is "loose cover").The gap is too large, will make ptfe material to the outside of the mold extrusion velocity slow down, material pressure on the conductor increases, often occur extrusion instability or cause conductor compression rolling and produce "pine" problem, and the conductor can not pass through the needle plug phenomenon.

Polymer material mixing extrusion technology and complete equipment

Mixing extrusion process is the only way for polymer materials, especially plastics, to move from products to industrialization. Modern polymer materials are developing towards high-performance polymer structural materials, new polymer functional materials and general polymer materials with low cost and high performance. 

High performance polymer structural materials are characterized by high specific strength, excellent corrosion resistance, abrasion resistance and easy processing, which are of great significance to the development of national economy and national security. Due to its unique functional and special type, new polymer functional materials have been widely used in the industrial fields such as ecological environment protection, information functionalization, biomedical equipment, material separation membrane, energy conversion and energy storage technology. High performance of general polymer materials and low cost of engineering plastics are still the focus of current research and development of polymer materials and an important measure to expand the application scope of general plastics and engineering plastics.

In addition to some processing properties of traditional polymer materials, the new polymer materials have many differences in physical and chemical properties. Appeared with the development of new polymeric materials, the fields of application broadening, to high polymer material mixing extrusion are also put forward higher request, the traditional mixing technology and equipment have not well some new high polymer material to meet the demand of the mixing, therefore, the development of new type mixing extrusion technology and equipment, to meet the needs of the new polymer materials to industrialization, mixing equipment BNR; at the same time, also is inevitable trend of the development of polymer processing equipment today.

1.       Application of twin screw mixing extrusion technology

Modern mixing and mixing extrusion technology is to blend existing polymer materials with a variety of polymers or add other materials to optimize the combination of different materials, so as to significantly improve the material properties, or give raw materials with new properties, adding new varieties to the polymer family. In the whole plastics industry, about 60% of the plastics have to be mixed and modified to produce new materials. Most of these complex processing processes are completed in the mixing equipment represented by the twin screw extruder. Using the same direction twin screw to mix extrusion has the following advantages:

(1) excellent mixing and plasticizing performance, which can fully guarantee the dispersion uniformity and performance uniformity of various materials after mixing, and is suitable for complex operations such as filling, blending, glass fiber reinforcement, reactive extrusion and volatile removal of various resins and plastics.

(2) cylinder and screw can realize "building block" combination, so as to achieve multi-purpose, multi-function.

(3) screw meshing, self-cleaning effect is good; The material achieves superior surface renewal effect and excellent exhaust performance, which can eliminate the gas or monomer generated in the mixing and plasticizing process.

(4) high screw speed, large production capacity, low power consumption per unit production, obvious energy saving effect.

Based on the above advantages, the co-directional twin-screw mixing extrusion technology has an irreplaceable advantage in polymer material processing equipment and occupies a leading position in polymer material modification production.

At present, the new type twin-screw compounding and the latest application of extrusion technology is mainly manifested in the following aspects: the preparation of nanometer material modification is high polymer material rigid Gao Ren type of low cost, high polymer alloy materials, electromagnetic shielding polymeric materials, novel polymer materials for degradable plastics, electronic packaging, new masterbatch and various functional masterbatch, etc., can also be used to new composite materials (such as wood plastic composite) the production and preparation of new materials, in addition, can also be used for polymer grafting, polycondensation of reactive extrusion. The industries involved include household appliances, automobiles, communications, electronic technology, national defense, aerospace, environmental protection, chemical industry, building materials, electric power, etc.

2.       Development of new polymer material extrusion technology with twin screw

At present, the development direction of new polymer materials, which are mainly composed of nanomaterials, degradable plastics, modified asphalt and wood-plastic composite materials, centers on the industrialization of these materials, and the same-direction twin-screw extrusion technology becomes the key to realize the industrialization. Compared with ordinary polyolefin materials, these materials have great differences in material system composition, molecular structure and rheological properties.

(1)     Nanomaterials are becoming a new type of materials developed by various countries in the world. From the preparation of nanometer masterbatch to the production of nanometer modified plastics, twin-screw extruder plays an irreplaceable role in the industrialization of nanometer plastics. Firstly, due to the particle size distribution of nanomaterials, the mixing extrusion and dispersion effects are required to be high. Secondly, the preparation of nanometer masterbatch for inviscid melt characteristics, low toughness, contains a large amount of gas extrusion and additives in the process of removing products of decomposition, and the traditional polymer under different state of plasticizing characteristics such as high brittleness, cooling and finished product process is different from ordinary polyolefin masterbatch process. 

     From mixing and plasticizing extruder to cooling and granulation, many innovative developments are needed. Therefore, the general cooling method of molten polymer cannot be adopted. The final product is produced by adopting the closed feeding mode with powder collection, adopting the new high-efficiency dense rotor element in the screw, setting buffer type exhaust mode in the cylinder, and adopting the route of belt conveying and cooling, pre-crushing and crushing in the material strip cooling and crushing.

(2)     There are a lot of starch in the development of starch filled degradable plastics, double degradable plastics and whole starch thermoplastic plastics. In addition to plasticizing and mixing them, exhaust dehydration and residence time distribution in the extrusion process have become problems that need to be solved when mixing and granulating. Therefore, according to the specific materials, the appropriate host screw length-diameter ratio, exhaust location and quantity, screw structure and arrangement, additive adding mode and adding point should be selected to test and determine the configuration; At the same time, the operation technology and technology also become the key problem of the degradation plastic twin-screw extrusion. The above key technologies can be based on the existing successful experience, combined with extrusion process experiment and results analysis, finally determine the extrusion process equipment configuration.

(3)     Modified asphalt has become a new direction of polymer material modification. Focusing on its application in highway construction, airport reconstruction and expansion projects, improving its temperature resistance and low temperature brittle property is the main direction of improving its application value. Because of the extensive molecular weight distribution and the structure of macromolecule, the modification of asphalt has not been much improved. Modified asphalt is very special, has both belong to the characteristics of the rubber plastic blending, but also has the content of the product post-processing, transport of twin screw extruder, mixing elements of development, such as extrusion granulation are put forward new requirements, need innovation to develop new type structure and configuration of the screw element, console, selected double screw part in all kinds of test parameters, such as screw length to diameter ratio, number and position of exhaust section, shear rate, extruding form and structure, etc.

(4)     In terms of material science, WPC is a new material with great potential. It is reported that plant fiber composites have been widely used in automobile industry, construction industry, transportation industry, aviation industry and so on due to their high mechanical properties, specific hardness, specific strength, sound absorption and biodegradability. In wood fiber, wood powder mixed with resin matrix, the mixture of different methods of wood fiber in composite material obtained by dispersing uniformity of difference is very big, to realize the industrialization of the wood plastic composite this new material production is the key to the extrusion process and special structure form of extruder, the technology innovation point lies in the segmented charging ways, special screw type structure, TME and ZME element, high torque gear transmission system, large screw length to diameter ratio and D/Di = 1.55 free volume, the one-step method of twin-screw extrusion production.

Preparation of UHMWPE fiber

UHMWPE, also known as high-strength high-modulus polyethylene, is currently one of the world's high-performance materials. Due to its comprehensive excellent properties such as corrosion resistance, wear resistance and low density, it is currently used in military protection materials, military mechanical materials, aerospace equipment and other military fields. The development of high-performance fiber is the foundation of a country's military equipment, and the advanced material can lead to the advanced military technology, which has become an important material foundation for the construction of a powerful modern country, and occupies a decisive position in the field of military materials worldwide.

1.    Properties of UHMWPE fiber 

UHMWPE fiber has excellent comprehensive properties, its relative density is small, can float on water. And UHMWPE fiber is the strongest fiber in the world at present. Compared with steel, UHMWPE fiber is more than ten times stronger than high-quality steel. In addition, UHMWPE fiber also has strong corrosion resistance, chemical resistance, wear resistance and other properties, comprehensive performance, UHMWPE fiber in many important fields in China play an important role.

1.1 Excellent mechanical properties

Compared with other high-performance fibers, UHMWPE fiber density is second only to conventional PE fiber and polypropylene fiber, and it is the optimal fiber material with the smallest density among bulletproof materials. It can reduce the weight of the material and achieve a lightweight effect while ensuring better bulletproof performance.

Compared with other properties, the tensile strength of UHMWPE is only second to that of PBO and polyaryl ester fiber, and it is only 0.1 different from that of polyaryl ester fiber. It can be seen that UHMWPE has excellent tensile strength.

Compared with other fibers, the initial modulus is only second to PBO and carbon fiber, which indicates that the fiber has a relatively good resistance to damage tension and is not prone to deformation. It is a kind of characteristic fiber with ultra-high specific strength and specific modulus, which plays an important role in bulletproof material.

1.2  Electrical insulation performance

UHMWPE fiber reflectance radar wave phenomenon is very few, with high conduction efficiency, enhance the dielectric constant of composite materials. Although the dielectric constant and loss value of polyethylene are the least among other materials, UHMWPE fiber has the performance that traditional polyethylene fiber can't reach, and it has better effect than general materials, so it is the preferred material for radar radome, with high quality and light effect.

1. 3  Weather resistance and wear resistance

UHMWPE fiber has excellent weather resistance and can keep the original high performance unchanged after a long time of illumination and harsh environment. At the same time, UHMWPE fiber has higher wear resistance and bending fatigue resistance than aramid fiber in high performance materials, so the wear resistance of this fiber is better than other high performance fibers. Due to its high wear resistance and easy processing performance, it has a good application prospect in the industrial field.

1. 4  Chemical corrosion resistance

The internal structure of UHMWPE fiber is relatively tight. It is precisely because of the high crystallinity and orientation of the molecular chain inside the fiber that the fiber has a strong chemical inertia. Therefore, under the acid and base state or the high and low temperature state, the fiber can keep its original performance unchanged for a long time, and still adapt to and play its value in the harsh environment.

1. 5  Self-lubricating properties

UHMWPE material compared with other engineering materials, UHMWPE material has very low friction factor, low friction factor makes the fiber itself better self-lubricating performance, it is the best material in plastic materials under the condition of no lubricant, so UHMWPE material is widely used in engineering, with very high use value. UHMWPE fiber is used in the operation of the machine, compared to the traditional steel and brass under the operation of the lubricant is better. Therefore, compared with ordinary materials, UHMWPE fiber not only saves the raw material cost, but also guarantees the excellent performance effect, so it has a higher use value.

2.  Preparation method of UHMWPE fiber

2.1  Gel spinning method

There are many methods to prepare high performance UHMWPE fiber, but due to the reason of solvent itself, the preparation of UHMWPE fiber can not be achieved. Gel spinning is the most ideal method. Gel spinning method is different from general solution spinning or wet spinning, generally using high molecular weight polymers as raw material, made of semi dilute solution as spinning dope, flexible molecule chain solution to tangles in the semi dilute solution, and then spinning, crystallization, high tensile stretch chain, after extraction treatment to times the thermal stretching, which is made with high strength and high modulus fibers. The gel spinning method has the following basic characteristics: (1) ultra-high molecular weight polymer is used as raw material;(2) use semi-dilute solution as spinning stock; (3) hyperthermal stretching was carried out, and the tensile ratio was greater than 30.

2.2  Plasticizing melt spinning method

Melt spinning is made of polymer melt by melt spinning and extruding. Plasticized melt spinning is on the basis of melt spinning, adding an appropriate amount of diluent to the polymer melt for spinning, through the twin screw mixed solvent, and then extruded, soaked in the extraction agent, and then repeated stretching can finally get high strength and high modulus polyethylene fiber.

2.3  High pressure solid state extrusion method

The principle of extrusion forming is that granular solid solvent is added to the extruder, the material barrel containing solid solvent is heated to the melting temperature, so that the solid material is molten, the molten agent is transported to the head of the machine with a fixed shape, and then after cooling and shaping, the final product is solidified. High pressure solid extrusion method is on the basis of extrusion forming high pressure melting, forming solvent, then through the jet hole, and then high tensile, and finally get high molecular weight polyethylene.

2.4  Surface crystallization method

Due to the slow growth rate of fibrous crystal, this method is seldom used in the preparation of UHMWPE fiber.

Polymer PTFE production process Ram-punch extrusion

With the development of technology and economy, ptfe has been applied in more and more fields, and has become an indispensable material to solve many key technologies in scientific research, military and civil fields and improve the production technology level. In order to continuously improve the production efficiency of polymer ptfe, we began to adopt the advanced production process, which is suitable for high viscoelastic material —— Ram-punch extrusion.

According to the principle of "forging", plunger stamping extruder mainly adopts plunger with small cross section area and high frequency stamping to push material into the barrel of extruder. Compared with traditional hydraulic column extruder, it has the characteristics of high stamping frequency, good melt plasticizing effect, good product quality, simple equipment and process.

According to the forming characteristics of Ram-punch extruder, the extrusion process is analyzed and studied. The physical model of the whole extrusion process of plunger ram extruder is established, which is divided into five sections: solid feeding section, melting section, shunt section, forming section and cooling section. The influence of die length and pressure vibration frequency on extrusion process was analyzed. Analysis results indicate that: although there are large fluctuation of pressure at the entrance of the melt, but on the whole pressure from inlet to outlet were reduced gradually, thus ensure the enough pressure to push the material extrusion, and the closer it gets to the finish mold outlet pressure and speed fluctuation is smaller, so it can ensure the continuity of extrusion, finally get good quality products. The length and stamping frequency of the die have certain influences on the extrusion pressure and speed. Due to the high viscosity of PTFE, a longer die should be selected, and the stamping frequency between 5-6hz is appropriate.

Ram plunger extrusion machining polymer PTFE are very new machining method , but in the process of material forming process, also cannot leave the material flow and deformation, rheological behavior and the law, understanding the process of molding process of reasonable selection, operation and optimization control and improve molding equipment has very important practical significance. Plunger stamping is not a steady-state machining method, and there is vibration in the stamping process. It is of great significance to study the behavior response of polymer under the action of vibration field, and to discuss how much impact the vibration field will have on the flow stability, so as to study the dynamic forming of polymer materials and optimize production.

Measurement for shear viscosity spectrum of polymer melts by using screw extruder capillary

Most polymer materials are processed in the melt state, which involves melt flow and deformation, which not only affects the processing process itself, but also affects the final performance of the product. Therefore, the study of rheological properties of polymer materials has been a hot topic. Accurate measurement of rheological parameters is the basis of in-depth study of rheological properties.

Shear viscosity is an important parameter to characterize the rheological behavior. The so-called shear viscosity of polymer melt is the ratio of shear stress and shear rate that melt is subjected to in the process of flow. Polymer melt causes pseudoplastic fluid, and its flow behavior has the characteristics of shear thinning. It is usually necessary to use the relationship curve between shear viscosity and shear rate, namely shear viscosity spectrum, to fully reflect the processing characteristics of polymer melt.

The basic method of measuring melt viscosity is to try to make the melt flow through a long and thin capillary tube, such as a round capillary tube. The shear stress can be calculated by measuring the pressure drop at both ends of the melt as it flows through the capillary tube. The shear rate can be calculated by measuring the flux of melt per unit time. Thus the melt viscosity can be obtained.

The conventional way to get the melt out of the capillary tube is to use piston propulsion. The advantage of this method is that it USES fewer test materials and can obtain higher shear stress. The high pressure capillary rheometer is based on this principle [4].However, the disadvantage of this test method is that the material cannot be tested under the actual processing conditions, and it is difficult to obtain the rheological properties of the polymer melt when it is processed. Especially in the study of blending modification of several polymer materials, the polymer melt needs the strong shearing action of screw to achieve the purpose of blending. High pressure capillary rheometer is not suitable for testing such materials.

The screw extrusion capillary rheological test device can solve the above problems. The device USES the propulsive force of the screw to make the polymer melt flow through the capillary tube. Therefore, the shear viscosity of polymer melt can be measured under conditions closer to real processing. This method is particularly suitable for the measurement of the rheological properties of thermoplastic materials and their mixtures. Because the measurement simulates the real experimental environment, the obtained test parameters can more accurately describe the behavior of materials in actual processing.

Shear viscosity spectra of polymer melts can be measured using specialized test instruments, such as high pressure capillary rheometers, or combined revolutions. However, these devices are expensive and limited in practical use, especially in the application of large-scale industrial production. In fact, it is not necessary to rely on the special test instrument, as long as the shear viscosity test principle, you can use a simple small single-screw extruder and capillary mold, constitute a low-cost shear viscosity spectrum test device. Combined with computer data processing, the shear viscosity spectrum of polymer melt can be easily and quickly obtained. This method is especially suitable for small and medium-sized enterprises to carry out product development and raw material inspection.

Polymer plasticized compounding extruder screw design

Screw is the most important part of extruder, can be said to be the heart of the extruder, it can directly affect the application of the extruder and production efficiency. The performance of screw determines the productivity, plasticizing quality, dispersion of filler, melt temperature and power consumption of an extruder. Through the screw rotation, the polymer plastic can be extruded, and the plastic can move, pressurize and obtain some heat from friction in the cylinder. During the movement of the cylinder, the plastic can be mixed and plasticized.

1.     The screw structure of polymer plasticizing and mixing extruder.

During processing, when the material moves forward along the screw, it experiences changes in temperature, pressure, viscosity, etc., which are different within the full length range of the screw. There are three physical states of   polymer plastic in extruder: glass state, high elastic state and viscous flow state. In order to adapt to the requirements of different states and according to the changing characteristics of the material, the screw can be divided into three sections: feed section, compress section and homogenize section.

The function of the feeding section is to feed the material supplied by the hopper to the compression section. During the movement of the plastic, it generally remains a solid state and partially melts due to heat. The length of the feeding section varies with the type of plastic. Compression section (transfer section) is the role of physical material pressure, so that the material from solid into molten, well out of the air in the material; In order to adapt to the characteristics of reducing the volume when pushing the gas in the material back to the feeding section, pressing the material and melting the material, the screw in this section should produce greater shearing effect and compression of the plastic. 

The function of the homogenizing section (metering section) is to feed the molten material to the machine head at constant volume (volume) and pressure so that it is formed in the mouth mold. The volume of the spiral groove in the homogenizing section is the same as that in the feeding section.

In order to avoid material retention in the end of the screw head dead corner, causing decomposition, screw head is often designed into a cone or semicircle; Some screw homogenization section is - the surface is completely smooth body called torpedo head, but there are also engraved grooves or milling patterns. The torpedo head has the function of stirring and controlling the material, eliminating pulsating (pulsating) phenomenon in the flow, reducing the thickness of the material layer with increasing the pressure of the material, improving the heating condition, and further improving the screw plasticizing efficiency. 

According to melt transport theory, melt flows in the screw homogenization section in four forms, and the flow of molten material in the screw groove is a combination of these four flows: positive flow -- plastic melt flows between the cylinder and the screw in the direction of the screw groove toward the machine head. Counter-current flow direction is opposite to the positive flow, which is caused by the pressure gradient caused by the resistance of the nose, porous plate and filter plate. The flow of the melt in a direction perpendicular to the thread wall affects the mixing and heat exchange of the melt during extrusion. Leakage flow - a backflow formed by the pressure gradient between the screw and the cylinder, along the axial direction of the screw. Different flow patterns have important effects on the mixing uniformity of polymers.

Screw diameter and the determination of structural form, mainly according to the production of product output, specifications, types of processed materials and various structural screw characteristics to determine. Generally, the feeding section of the screw has a deeper groove and the groove depth is unchanged, compression section (melt section) of the screw groove depth along the direction of discharge from the deep to shallow, metering section (homogenized section) of the screw has a shallow groove and the groove depth is unchanged.

2.     The screw material.

Screw is the key part of extruder, as the material of screw must have high temperature resistance, wear resistance, corrosion resistance, high strength and other characteristics, at the same time should have good cutting performance, heat treatment residual stress, small thermal deformation and other characteristics. For extruder screw material, there are specific requirements as follows:

(1)   High mechanical properties. To have enough strength, to adapt to high temperature, high pressure working conditions, improve the service life of the screw.

(2)   Good machining performance. Good machining performance and heat treatment performance.

(3)   Good corrosion and wear resistance.

(4)   Easy to draw.

Study on Sintering of Ptfe

From the perspective of the three factors that determine the properties of PTFE products -- molecular weight, crystallinity and voidage, the voidage is mainly affected by the preforming pressure, and the molecular weight and crystallinity all change with the different sintering conditions. Therefore, sintering process conditions play a decisive role in the final properties of products such as density, hardness, permeability and mechanical properties.

Wang ping found that the sintering process of PTFE was affected by the rising and falling speed, sintering temperature and sintering time. The larger the product, the slower the speed of rising and cooling, the longer the sintering time. The sintering temperature of suspension resin is higher than that of dispersion resin. The sintering temperature of pure material products is higher than that of filled products. In general, the rate of warming is faster than the rate of cooling. In the same sintering furnace, pure material and filling products cannot be mixed; Products with different sintering conditions cannot be mixed. Products of different raw materials cannot be mixed. Taking the production of 3-layer molded circular plate with diameter of 1 m, thickness of 20 mm, double layer as pure ptfe and middle layer as filled ptfe as an example, the compression strength, bending strength, hardness and other mechanical properties of the circular laminated plate produced by this technology have been greatly improved.

Liu xianlan studied the forming process characteristics, forming method and mold design characteristics of PTFE, analyzed the defects and causes of PTFE products produced by cold pressing and sintering, and put forward the treatment methods. PTFE can be molded by a variety of preforming processes, such as molding, extrusion, hydraulic molding, push molding and secondary processing, and then sintered to the final product.PTFE molding is mostly made of suspended resin. When the thickness of sheet is less than 1.5mm, disperse resin is used. Its technological process: resin - sieve (suspension resin after pounding, loose, and the 20 mesh mesh sieve) - press (PTFE powder loading the mould under pressure from 20 to 35 MPa, after press compaction forming) - sintering (in 370 ~ 380 "C temperature sintering in sintering furnace) - moulded products (under free state within the mold or after cooling to finalize the design as required by the board, rods, tubes, gaskets and packing products, etc.).Hydraulic method is also called the equilibrium method or rubber molding in its operating process is: put rubber bag in die - connected to the water pump, filling the water swell the rubber bag into a cylindrical - resin evenly join between bag and external mold mold closing - continue to gradually increase the water pressure, water filling up to 12 ~ 13 mpa pressure maintaining 30 min: after water - decompression, ripping, sintering, cooling is the use of bright and clean appearance. Push is also called the paste extrusion molding, 20 ~ 30 mesh sieve dispersion resin and organic liquid (such as toluene, petroleum ether, the solvent oil) mixture 1:5 paste mixture, preloading into thick wall cylinder billet, push into the compressor cylinder, heating, with a plunger push molding, after drying in the 360 ~ 380 ° C temperature sintering, after cooling products have strong push tube, rod, etc.Extrusion molding can be divided into two types: screw extrusion and plunger extrusion. The pre-sintered resin after crushing and sifted is added to the material cylinder. Through screw rotation or reciprocating push of plunger, the raw material is transported to the extruder at the same time of compaction.

Wang ping studied the forming process of PTFE foam material. Suspended polytetrafluoroethylene is used as raw material, and condensed cyclic aromatic hydrocarbons are selected as pore-forming agent. After mixing, preforming products are preformed and sintered. At the initial stage of sintering, drying process is adopted to make pore-forming agent escape, and then resintering stage is entered. Foam materials with different dielectric constants can be prepared in different proportions to meet various requirements.

Chen xu et al. conducted compression test and sintering test on PTFE, discussed the relationship between density, compression strength and compression modulus, and analyzed the compression strength of specimens under different sintering processes, and obtained more appropriate molding pressure and sintering process. The results showed that the compression strength of PTFE decreased with the increase of pressing pressure, and the compression modulus increased with the increase of pressing pressure. The molding pressure was 27.5mpa, sintering temperature was 380 C, and the insulation time was 4h.

In order to overcome the disadvantages of pure ptfe, such as poor abrasion resistance and large thermal expansion coefficient, Raytheon studied the bronze-filled particles in ptfe, and expanded the application scope of ptfe. The conventional warm pressing molding of ptfe is characterized by long cycle, poor performance, low dimensional accuracy and smoothness, while the warm pressing molding in this study has fewer working procedures, short cycle and significantly improved mechanical properties.

Study on preparation and technology of ptfe hollow fiber membrane

Hollow fiber membrane is widely used in traditional and new membrane separation components such as ultrafiltration, microfiltration, reverse osmosis and gas separator due to its small area, high filling density, high utilization rate, easy to enlarge and easy to clean.In addition, polytetrafluoroethylene hollow fiber membrane has high mechanical strength, acid and alkali resistance, high and low temperature resistance, low friction coefficient on the surface, so it has great potential in special filtration, gas absorption, ozone dissolution filtration, membrane distillation and other fields.PTFE hollow fiber membrane was prepared by using PTFE dispersion resin as raw material and adding exxonmobil Isopar series lubricants through extrusion and stretching molding.

Average extrusion pressure, pore diameter and bubble point pressure, porosity, water flux, contact Angle, SEM and DSC were used to characterize the structure and performance of PTFE hollow fiber membrane.The experiment mainly discusses the influences of lubricants (types and ratios), extrusion process (compression ratio, length-diameter ratio and cone Angle) and tensile sintering process on PTFE structure and performance, and optimizes the process parameters to provide guidance for PTFE hollow fiber membrane production.

Specific research contents are as follows:

(a)     the experiment changed the lubricant parameters (including the type and ratio of lubricants) and prepared PTFE hollow fiber membrane through the process route of "mixing → pre-molding → extrusion → stretching → sintering → natural cooling".The experiment explored the influence of lubricant type and ratio on the structure and performance of PTFE hollow fiber membrane, and obtained the best combination of lubricant type and ratio and optimized lubricant.

(b)     by changing the parameters of extrusion process molds, the influences of RR, L/D and alpha on extrusion pressure, membrane fracture strength, average pore diameter, bubble point pressure, porosity and water flux were explored to obtain the best extrusion parameters.

(c)     By adjusting the tensile process parameters (tensile multiple and tensile temperature) and sintering process parameters (sintering temperature and sintering time), the influences of tensile sintering process on the average pore diameter, bubble point pressure, porosity and water flux of PTFE hollow fiber membrane were explored to obtain the optimal tensile sintering process parameters and optimize the tensile sintering process.

Experimental results show that:

(1)     PTFE hollow fiber membrane has small average pore diameter, high bubble point pressure and porosity, large water flux fracture strength and contact Angle, and low extrusion pressure in the extrusion process.When the lubricant content is too high or too low, the structure and properties of PTFE hollow fiber membrane will be adversely affected to some extent.

(2)     When RR=185, L/D=20, and alpha =40°, the extrusion pressure is low, the fracture strength is large, the average pore diameter is small, the bubble point pressure is high, the porosity is large, and the water flux is high, which can be used as the extrusion process parameters of excellent PTFE hollow fiber membrane.

The influences of tensile and sintering processes on the microstructure and properties of PTFE hollow fiber membrane are as follows: with the increase of tensile multiple, the average pore size and porosity of PTFE hollow fiber membrane are large, the bubble point pressure is small, and the water flux is large.With the increase of tensile temperature, the average pore diameter and water flux of PTFE hollow fiber membrane increase, the porosity increases, and the bubble point pressure decreases.With the increase of sintering temperature, the pore diameter, bubble point pressure and water flux of PTFE hollow fiber membrane decrease, and the porosity has no obvious change rule.With the increase of sintering time, the average pore diameter, porosity and water flux of PTFE hollow fiber membrane increase, and the bubble point pressure decreases.

The drawing process significantly reduces the crystallinity of PTFE products, while the sintering process further reduces the crystallinity of PTFE products.When the tensile multiple is 100%, the tensile temperature is 300℃, the sintering temperature is 320℃ and the sintering time is 5min, the average pore diameter of hollow fiber membrane is small, and the bubble point pressure, porosity and water flux are large.